The operation of conventional plasma arc torches is well understood by those in the art. The basic components of these torches are a body, an electrode mounted in the body, a nozzle defining an orifice for a plasma arc, a source of ionizable gas, and an electrical supply for producing an arc in the gas. Upon start up, an electrical current is supplied to the electrode (generally a cathode) and a pilot arc is initiated in the ionizable gas typically between the electrode and the nozzle, the nozzle defining an anode.
A conductive flow of the ionized gas is then generated from the electrode to the work piece, wherein the work piece then defines the anode, and a plasma arc is thus generated from the electrode to the work piece. The ionizable gas can be non-reactive, such as nitrogen, or reactive, such as oxygen or air.
A longstanding problem with conventional plasma arc torches is the wear of the electrodes. Typically, the electrodes include a hafnium or zirconium insert. These materials are desired for their material properties when cutting with a reactive gas plasma but are extremely costly and require frequent replacement.
While not intending to be bound by any particular theory, it is believed that multiple factors contribute to electrode wear. For example, during operation of the torch, the insert material becomes extremely hot and enters a molten state as electrons are emitted from the high emissivity material to form the arc. Eventually, a hole or cavity may form at the exposed emission surface of the insert. This cavity, typically concave in shape, is formed due to the ejection of the molten, high emissivity material from the insert during operation. The ejection of material can occur at various times during the cutting process such as e.g., during initial start-up creation of the plasma arc, during cutting operations with the arc, and/or while or after stopping the plasma arc. The ejection of molten material not only provides wear of the insert but can also wear other parts of the torch such as the nozzle. More particularly, the molten material from the insert may be ejected from the electrode to the surrounding nozzle, which in turn can cause the arc to improperly attach to, and thereby damage, the nozzle.
Accordingly, an electrode having one or more features for improving wear would be useful. More particularly, an electrode that can reduce or minimize the ejection of molten material from the insert would be beneficial. Such an electrode that can also reduce or minimize damage to the portion of the electrode surrounding the insert would also be useful.